As a representative of the third generation of semiconductor materials, gallium nitride (GaN) has many excellent characteristics, such as high critical electric field for breakdown, high electron mobility, high two-dimensional electron gas concentration, and good high temperature working ability, etc. The third generation of semiconductor devices based on gallium nitride, such as high electron mobility transistor (HEMT), heterostructure field effect transistor (HFET), and the like, have been put into use, and have obvious advantages especially in areas requiring high power and high frequency, such as radio frequency and microwave, etc.
For HEMT or HFET devices, a channel conduction from the source to the drain is mainly realized by the two-dimensional electron gas (2DEG) at the interface between aluminum gallium nitride (AlGaN) and gallium nitride (GaN). However, since both AlGaN and GaN are approximate to insulators and have a relatively large contact resistance, the on-resistance of the entire device is large, which limits the application range of the device.